Hi Brant, My version of Orthodont doesn't seem to have as many levesl of age as yours but the general idea is
> library(MEMSS) > data(Orthodont) > library(reshape) # could use reshape function in stats package instead of cast > c.orth <- as.data.frame(cast(Orthodont, Subject + Sex ~ age, > value="distance")) > names(c.orth)[3:6] <- paste("age", names(c.orth)[3:6], sep="_") > cor(c.orth[3:6]) age_8 age_10 age_12 age_14 age_8 1.0000000 0.6255833 0.7108079 0.5998338 age_10 0.6255833 1.0000000 0.6348775 0.7593268 age_12 0.7108079 0.6348775 1.0000000 0.7949980 age_14 0.5998338 0.7593268 0.7949980 1.0000000 Best, Ista On Mon, Feb 28, 2011 at 12:07 AM, Brant Inman <brant.in...@mac.com> wrote: > R-helpers: > > I would like to measure the correlation coefficient between the repeated > measures of a single variable that is measured over time and is unbalanced. > As an example, consider the Orthodont dataset from package nlme, where the > model is: > > fit <- lmer(distance ~ age + (1 | Subject), data=Orthodont) > > I would like to measure the correlation b/t the variable "distance" at > different ages such that I would have a matrix of correlation coefficients > like the following: > > age08 age09 age10 age11 age12 age13 age14 > age08 1 > age09 1 > age10 1 > age11 1 > age12 1 > age13 1 > age14 1 > > The idea would be to demonstrate that the correlations b/t repeated measures > of the variable "distance" decrease as the time b/t measures increases. For > example, one might expect the correlation coefficient b/t age08 and age09 > to be higher than that between age08 and age14. > Is there a function that can calculate such correlation coefficients of a > repeatedly measured variable "y" ("distance" in the Orthodont dataset) > across some category "x" ("age" in the Orthodont dataset)? > > Thanks, > > Brant > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- Ista Zahn Graduate student University of Rochester Department of Clinical and Social Psychology http://yourpsyche.org ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.